- Group “Drug” : a Man in microgravity is the sole experimental model available to test the rapid occurrence of osteoporosis on a healthy subject. Osteoporosis, or porous bone, appears whenever the rate at which the bone material is replaced falls below that of resorption, thus creating a bone fragility and an increased risk of fracture (hip, spine and wrist essentially). It appears generally after menopause, when associated with aging and a lack of physical activity. The pamidronate (Aredia®) is a drug present on the market since many years, used for the treatment of several bone pathologies. This drug will be tested on the 9 volunteers of this group, to demonstrate its efficiency in treating of bone modifications. This drug (60mg) will be infused intravenously 14 days before bed rest.